Reset the key, and resume waiting for events.Retrieve each pending event for the key (there might be multiple events) and process as needed.You can obtain the file name from the key. Retrieve the key from the watcher's queue.When an event occurs, the key is signaled and placed into the watcher's queue. Implement an infinite loop to wait for incoming events.You receive a WatchKey instance for each directory that you register. When registering a directory, you specify the type of events for which you want notification. For each directory that you want monitored, register it with the watcher.Create a WatchService "watcher" for the file system.Here are the basic steps required to implement a watch service: You can use it as is, or you can choose to create a high-level API on top of this mechanism so that it is suited to your particular needs. The WatchService API is fairly low level, allowing you to customize it. Creating a Watch Service and Registering for Events.When an event comes in, it is handled as needed. The registered process has a thread (or a pool of threads) dedicated to watching for any events it has registered for. When the service detects an event of interest, it is forwarded to the registered process. When registering, you tell the service which types of events you are interested in: file creation, file deletion, or file modification.
This API enables you to register a directory (or directories) with the watch service. The package provides a file change notification API, called the Watch Service API.
It does not scale to applications that have hundreds of open files or directories to monitor. One way to do so is to poll the file system looking for changes, but this approach is inefficient. To implement this functionality, called file change notification, a program must be able to detect what is happening to the relevant directory on the file system.
JEdit Dialog Box Showing That a Modified File Is Detected The following sample dialog box shows how this notification looks with the free editor, Have you ever found yourself editing a file, using an IDE or another editor, and a dialog box appears to inform you that one of the open files has changed on the file system and needs to be reloaded? Or perhaps, like the NetBeans IDE, the application just quietly updates the file without notifying you.
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